I 



Bulletin No. 43. 

U. S. DEPARTMENT OF AGRICULTURE 

X X OFFICE OF EXPERIMENT STATIONS. 

557 

or 



LOSSES IN BOILING VEGETABLES 



COMPOSITION AND DIGESTIBILITY 
OF POTATOES AND FOGS. 



H. SNYDER, B. S., ALMAH J. 7 XS3* M. D., AND A. P. BRYANT, M. S. 




WASHIXGTOX: " 

GOVERNMENT PRINTING OFFICE. 




Class -T X 5$7- 
Book__iti- 



Bulletin No. 43. 



U. S. DEPARTMENT OF AGRICULTURE. 

OFFICE OF FXPESIMENT STATIONS. 



6" 2- o 



LOSSES IN BOILING VEGETABLES 



COMPOSITION AND DIGESTIBILITY 
OF POTATOES AND EGGS. 



a OTYHEH, B. S, ALMAH J. FBISBY, M . D ., AND A . 



P. BRYANT, M. S. 




WASHTOGTOK: 

GOVERNMENT PRINTING OFFICE, 
1897. 

<2 -^(f^- "2- 



LETTER OF TRANSMITTAL. 



U. S. Department of Agriculture, 

Office of Experiment Stations, 

Washington, D. C., May 15, 1897. 

Sir : I have the honor to transmit herewith a report on the loss of 
nutrients in boiling potatoes, carrots, and cabbage, and the composi- 
tion and digestibility of potatoes and eggs, by Prof. H. Snyder, Almah J. 
Frisby, M. D., and A. P. Bryant, M. S. These investigations consti- 
tute a part of the inquiries made with the funds appropriated by Con- 
gress "to enable the Secretary of Agriculture to investigate and report 
upon the nutritive value of the various articles and commodities used 
for human food," and were carried on under the supervision of Professor 
Atwater, special agent in charge of nutrition investigations, in accord- 
ance with instructions given by the Director of this Office, 

The greater part of the food of man is prepared for use by cooking, 
yet the changes which various foods undergo during the process and 
the losses which are brought about by cooking have been little studied. 
This question has a wide practical application as well as scientific 
interest. In determining the nutritive value of various articles of food, 
digestibility is an important consideration. Perhaps no feature of the 
subject is more discussed. Nevertheless very few experiments with 
man to determine the digestibility of various foods have been made. 
Almost all information has been derived from artificial digestion experi- 
ments which approximate more or less closely digestion in the body. 
It is by no means certain that the two processes give the same results. 
Digestion experiments with man were believed to be necessary, and 
a diet in which potatoes were the chief ingredient was selected for 
experimental purposes. 

Professor Snyder's work was carried on in the laboratory of the Col- 
lege of Agriculture of the University of Minnesota; that of Dr. Frisby 
and Mr. Bryant in the chemical laboratory of Wesleyan University, 
Middletown, Conn. 

This report is respectfully submitted, with the recommendation that 
it be published as Bulletin No. 43 of this Office. 
Respectfully, 

A. C. True, 

Director. 

Hon. James Wilson, 

Secretary of Agriculture, 



CONTEXTS. 



Page. 
LOSS OF NUTRIENTS IN BOILING POTATOES, CARROTS, AND CABBAGE. By 

H. Snyder, B. S 7 

Introduction 7 

The three principal classes of nutrients in foods 7 

The effect of cooking on the nutrients of foods 8 

Experiments "with potatoes 9 

Composition of potatoes 9 

Cooking tests 11 

Discussion of results 13 

Conclusions 14 

Experiments with carrots 15 

Composition of carrots 15 

Cooking tests 15 

Conclusions 17 

Experiments with cabbage 17 

Composition of cabbage 17 

Cooking tests 18 

Conclusions 19 

General summary 19 

The digestibility of potatoes and eggs. By H. Sxyder, B. S 20 

Introduction 20 

Digestibility of boiled eggs in pepsin solution 20 

Digestion experiment on man with a diet of potatoes, eggs, milk, and 

cream 21 

Discussion of results 23 

The composition of different parts of the potato and the loss of 
nutrients during the process of boiling. by almah j. frisby, m. d., 

and A. P. Bryant, M. S 25 

Introduction 25 

Composition of different parts of the potato 26 

Sampling 26 

The analyses 27 

The protein factor 28 

Amonnt of solid matter in the j uice of the potato 29 

Loss of nutrienvs in boiling 29 

Conclusions 31 



ILLUSTRATIONS. 



Fig. 1. Colls of a raw potato with starch grains in natural condition 8 

2. Cells of a partially cooked potato v 

3. Cells of a thoroughly boiled potato 9 

4. The composition of the potato and the loss of nutrients when boiled 

with the skin removed 11 

5. The composition of the carrot and the loss of nutrients when boiled. . IT 

6. The composition of the cabbage and the loss of nutrients when boiled . 19 

7. Transverse and longitudinal sections of the potato 36 

G 



LOSSES IN BOILING VEGETABLES, AND THE COMPOSITION 
AND DIGESTIBILITY OE POTATOES AND EGGS. 



LOSS OF NUTRIENTS IN BOILING POTATOES, CARROTS, AND 
CABBAGE. 

By H. Snyder, B. S., 

Chemist, Minnesota Agricultural Experiment Station, and Professor of Agricultural 

Chemistry, College of Agriculture, University of Minnesota. 

INTRODUCTION. 

THE THREE PRINCIPAL CLASSES OF NUTRIENTS IN FOODS. 

The nutritive ingredients of foods are commonly divided into three 
general classes, namely, nitrogenous substances to which the general 
term protein is applied, fats, and carbohydrates. 

The nitrogenous substances. — The nitrogenous substances include (1) 
the albuminoids, of which egg albumen is a well-known example ; (2) the 
so-called gelatinoids, of which gelatin may serve as a type; and (3) 
the amids; i. e., synthesis and cleavage products of various kinds. 

The vegetable albuminoids are to a large extent different from 
those found in animal foods. They appear to be more variable in 
composition, and less is known concerning their chemical composi- 
tion, structure, and digestibility. 

The fats. — The amount of dry matter dissolved out of a substance by 
continuous treatment with ether is designated as fat. It forms a large 
part of animal foods, but in vegetable foods, with the exception of some 
seeds and nuts, the proportion is very small. 

The carbohydrates. — This class includes the sugars, starches, woody 
fibers, cell walls, etc., of the vegetable foods. Carbohydrates are found 
in but few animal foods, with the exception of milk, and when present 
are in very small quantities. In vegetable foods, on the contrary, they 
form the major part of the nutritive matter. The principal constituent 
of vegetable carbohydrates is starch. The starch grains are usually 
inclosed in thin cells, the walls of which may be composed of more or 
less fibrous material. 

The digestibility of the carbohydrates depends upon the proportion 
of sugar and starches to cell walls or fiber. The sugars are more easily 
digested than the starches, since the latter must be changed to sugar in 
the process of digestion before it can be assimilated by the body. Both 




• potato with bUtrc 
condition. 



the starches and the sugars, however, sire probably completely digested, 
but the cell walls, tin* framework of the substance, are not so easily 
digested ; in fact, while 98 to LOO per cent of the starches and sugars 

may be digested, the di a 
Utility of these cell walls, <>r 
fiber as it is called, may vary 
all the way from 30 to 70 per 
cent. 

Mil. I 1 I l.« I <H COOKING ON Mil 

\i I l:ll ST8 "l i I 

Some of the albuminoids 
are soluble in water, and 

nearly all in dilute saline 
solutions. II eating coagu- 
g the albuminoids and 
renders them insoluble. 
< looking, therefore, preserves 
albuminoids from loss. It 
meat is put into cold water 
and then brought to the boil 
ing point more or less of the 
albuminoid material will be dissolved and some of the most expensive 
part of the food will be lost unless the soup is utilized also. If put 
directly into hot or boiling water the soluble albuminoids on the surface 
will be coagulated, and this 
loss will be largely pre 
vented. 1 The same princi- 
ple is probably applicable 
to vegetables also. 

Besides rendering sol- 
uble albuminoids insoluble, 
cooking makes others of 
the nitrogenous substances 
more digestible, and iu the 
case of meats loosens the 
libers of connective tissue. 
rendering it tender and 
more palatable. Unless the 
degree of heat is great 
enough to cause scorching, 
fats are doubtless little af- 
fected by cooking. 

The carbohydrates are 
much more easily digested in the cooked than in the raw state. In the 
raw food the sugars and Btarches are inclosed in cells. Very little of 




T. B. Dept. Agr., Farmers' BoLSi. 



the cellulose of the cell walls is digested, by man. The cell contents, 
therefore, are often excreted unchanged. Cooking bursts these cell 
walls, thus exposing the inclosed sugars and starches to the action of 
the digestive juices. The starch granules also swell up and burst on 
cooking, exposing more surface to be acted upon. Starch is to a slight 
extent changed to dextrin by dry heat, and possibly, also, by heating 
with water. Since the majority of vegetable foods, however, consist 
largely of starches and 
have very little sugar in 
them, the loss of carbohy- 
drates would presumably 
not be very great during 
boiling. 

The effect of boiling upon 
the cells of the potato is 
shown in figs. 1, 2, and 3. 1 

Several years ago Kath. 
erine Williams reported 2 
an extended study of the 
composition of a number of 
cooked and a few raw vege- 
tables. Ultimate and prox- 
imate analyses of the vari- 
ous vegetables were made 
and the fuel value deter- 
mined. Many cooked veg- 
etables have been analyzed in connection with the food investigations 
undertaken by this Department and by other investigators. 

Comparatively few attempts have been made to learn the changes 
which take place in vegetable foods on cooking, or the extent of these 
changes. As the water in which vegetables are boiled is usually thrown 
away, any matter which was in solution would be wasted. Experiments 
were therefore undertaken with potatoes, carrots, and cabbage for the 
purpose of studying the loss of nutrients when boiled, under a number 
of different conditions. These vegetables were selected as the best 
representatives of tubers, roots, and pot herbs. 

EXPERIMENTS WITH POTATOES. 
COMPOSITION OF POTATOES, 

According to Lawes and Gilbert, 3 the conrposition of the flesh of the 
potato differs from that of the juice. Although the flesh contains 85 
per cent of the total water- free substance, it contains but 15 per cent of 

J U. S. Dept. Agr., Office of Experiment Stations Bui. 21, p. 88; from Marcker's Stu- 
dien in der Spiritusfabrikation. 

2 Jour. Chem. Soc. [London], 61 (1892), p. 226. 

3 "On the growth of the potato," p. 26, Rothamsted Memoirs, vol. 6. 




Eig. 3.— Cells of a thoroughly boiled potato. 



10 

the nitrogen. The remainder, 85 per cent, is in the juice. Of this 49 
percent is in the form of albuminoid and 36 per cent in the form of 

nonalbuininoid nitrogen. 

The proportion of albuminoid and nonallmminoid nitrogen varies 
greatly according to different writers. E. Schulze and BarbierPand 
E. Schulze and B. Kugster- give, as the result <>f five analyses, from .'*."> 
to 56 percent of oonalbuminoid nitrogen. O. Kellner gives It to 58 
per cent of nonalbnminoid nitrogen, and A. Morgen from 30 to 52 per 
cent, making 4o per cent ;is a fair average of the amount of nonal- 
bnminoid nitrogen and 55 per cent for the amount oi albuminoid nitro- 
gen present in potatoes. In the experiments here reported the figures 
obtained were nearly the reverse of these latter, as the average of the 
two analyses made gave 40 per cent of albuminoid and 60 per cent of 
nonalbnminoid nitrogen (see also p. 29). It is evident that in boiling 
the loss of a considerable portion of this albuminoid nitrogen may 
occur. 

There is also a possibility of loss of inorganic and organic salts dur- 
ing cooking. Probably about 85 per cent of the potash of the potato, 
as well as the larger part of the citric aeid. is in the juice. The total 
amount of citric acid, however, is small. While potash salts and cit- 
rates have no real nutritive value, they appear to be of some considerable 
medicinal or tonic value and give "relish" to the food. No attempt was 
made to determine the loss of fat and liber in boiling. It would be 
presumably, very small. 

Three experiments on the effect of cooking on the composition of pota- 
toes were made. In the first experiment (A) the skins were removed and 
the potatoes soaked three and five hours, respectively, and cooked in 
distilled water, which was cold at the beginning of the test. In the 
second experiment (B) the skins were removed and the potatoes, with- 
out previous soaking, were cooked in (1) distilled water soft water), 
(2) alkaline water, (3) limewater (hard water . which was in each case 
cold at the beginning; in (4) distilled water, (5) alkaline water, ami (6) 
limewater. which was in each case hot at the beginning of the test. 
In the third experiment (0) the potatoes were not peeled and were 
cooked without previous soaking in distilled, alkaline, and limewater, 
which was cold at the beginning of the test, and in distilled, alkaline, 
and limewater, which was hot at the beginning of the test. 

About two bushels of potatoes of a uniform character were divided 
into lots of about a kilogram 1' pounds each. An apaly8iswas made 
of the whole potato, including the skin. This was assumed to repre- 
sent the Composition of all the potatoes used iii the experiments except 
those which were soaked before boiling. In this latter case half of each 

"Landw. Vers. Stat., 21 1878 . p. 63. 

'Ibid., 27 L882), }>. :::.:. 

'■ Konig, ('lie ii lie der menschlicheo Nahrmigs- and < fonusamittel, 3ded., [I, p. 631. 



11 

of the peeled potatoes used in the experiment was taken as a sample 
and analyzed. 

The methods of analysis used were substantially those adopted by 
the Association of Official Agricultural Chemists, and were as follows : 

Xitro</en. — In order to ascertain the relative proportion of albumi- 
noids and extractives or amids the nitrogen was determined, (1) as the 
total nitrogen by the Kjeldahl method, and (2) the albuminoid nitrogen 
by the Stutzer method. The results for albuminoid nitrogen are with- 
out doubt too low, as the copper proteid dissolved to a slight extent in 
the moderately warm solution when filtered and separated out on stand- 
ing. If filtered when cold the filtration was so slow that fermentation, 
with a consequent loss of the copper proteid, would begin before the 
filtration was completed. 

Starch. — Starch was determined by inversion with boiling hydro- 
chloric acid and water and estimating the amount of copper in Fehling's 
solution precipitated by the resulting dextrin. 

Fat, fiber, and ash. — These were determined in the usual way in the 
fresh material. 

The accompanying table shows the composition of the potatoes used 
in these experiments, and gives also the composition as obtained by 
former analyses at the University of Minnesota, 1 the average of all 
American analyses, 2 and the average of European analyses. 3 

Composition of jiotatoes. 











Carbohydrates. 


Ash. 


££ *—■ ^rt' ■*" 1 & "* 
ses. gen. " 


Fiber. 


Starch. 


Nitro- 
gen - 
free ex- 
tract, a 


Used in Experi- 


Per ct. Per ct. Per ct. 

1 78. 0. 15 0. 35 


Per ct. 
2.2 


Per ct. 


Per ct. 


Per ct. 


Per ct. 


Per ct. 
0.9 


TJsed in Eperi- 
nients B and C. 

Average other 
Minnesota anal- 
yses 

Average all Amer- 


1 77. 2 .15 .40 

20 75.5 .20 j .40 
86 78.0 ' 


2.5 

2.5 

2.2 
2.1 


0.1 

.1 

.1 
.1 


0.2 
.3 


16.4 
19.9 


19.3 

20.9 
18.8 
21.7 


.9 

1.0 
.9 


Average " Euro- 
pean analyses .. 


178 75.0 &.19 .34 


.7 




1.1 



a 100 less the stun of the percentages of water, protein, fat, and ash. 
& Calculated, allowing 45 per cent to be albuminoid. 

COOKIXG TESTS. 

The potatoes were boiled in a metal kettle over a gas flame at 
about the same rate as when cooked in the kitchen. The uncooked 
potatoes were weighed, and the water in which they were cooked was 
also weighed and analyzed. The total amounts of dry matter, albumi- 
noid nitrogen, total nitrogen, starch, and ash that were removed in 



1 Minnesota Sta. Bui. 42. 

2 From an unpublished compilation of analyses of American food products. 
3 Konig ; Chemie der menschliclien Nahrungs- und Genussmittel, 3d ed., II, p. 626. 



12 

cooking 100 parts of fresh potatoes was then calculated. The results 
of each of the three experiments arc given in the following table: 



of matter in cooking poUttom. 





1 
| 

— 
--< 
- 


l.n- of mattei In Eresli 
potato s. 


■titoeat 




Method of preparation and 
cooking. 


1 

£ 
>> 




ig 

,032 


-. -' 


- 
■ 

i. 




u 

£ 

n 


— 

1 = 

■1 :l 

- : 

£ - 
4* 


P = 

_ i 


— 


< 


A. Skins rt moved .■ soaked be- 

/or- cooking. 

Soaked 3 hours; distilled 


Grams. 

753 

603 


1.4.-. 
1.4H 


0.035 
.040 


F.rt. 
0.161 


1 '.r(. 


0.41 
.28 


J'.rt. 

6.6 
6.4 


r.rt 

26.7 


P.ct. 


r.,-t. 




Soaked 5 hours: distilled 

water, cold at start 


:;i. l 






1.43 

.63 
.74 


.038 

.007 
.006 


.181 
.080 




0.16 
.16 


.35 
.15 


«;.:. 25.0 


51.8 




81 :< 




843 

939 






l.o 




]',. Skine removed; not soaked. 

Distilled water, cold at start . 
Do 


2. 8 4. 7 

3.2 4.o 


13.8 


19.6 






.68 


.006 


.068 


. 16 


.16 


3.0 4.3 16.9 


1.0 


17.9 








Alkaline water, cold at start. 
Do 


952 


.68 
.67 


.016 
.011 


.055 
.061 


.15 

. l'.» 


.17 

.17 


3."' 10.7 L3.fr 
2.9 | 7.:; 16.7 


.9 
1.2 


18.5 
18.5 







.67 | .014 


.065 


.17 


.17 


2. 9 9. 15. 2 


1.0 


18.5 








Lino-water, cold at start 

Do 


907 
979 


.70 .on 

.79 .015 


.055 
. 087 


.14 
.17 


.18 

.19 


3.1 7.3 13.8 
8.5 lo.O 16.7 


.9 

1.0 




Average 


^^= 


.::> .013 


.061 


• 16 


= 


3.3 


9.0 15.3 


L0 
1.0 






3.1 














Distilled water, hot at start.. 

Do 


939 
1,052 


.72 

.52 .004 


.033 


.11 

.10 


.17 

- 




.7 


18.5 


Average 




.62 .004 .025 

.71 .003 .033 
.80 .im.4 .041 


.10 


.13 
.19 


2.7 7.8 

3. 1 

I : 10. 1 


.6 

1 

l.'J 




Alkaline water, hot at start.. 
Do 


988 
970 


.17 
.19 


20.7 


Average 




.70 .003 .087 


.18 


.21 


3. 3 2. 3 9. 2 


1.1 


22.3 








Lixnewater, hot at start 

Do 


1, 043 


1.15 .OCX 


.26 

.17 


.15 
. 19 


5. 1 i 
1 


1.6 


16.3 






H06 


.031 


.22 


.17 


























- 1 


1.0 















.03 








0. 8kii . 

Distilled water, cold at star! 
Do 




.li Tnwe 

.11 Ira. •• 


.004 


.5 .1 


1 -J 


7 6 






.13 'I' rare .006 




.05 


.6 1 












Alkaline water, cold at -ia;t 

Do 




- 
.12 


Tracei .004 


.03 


I 






\ \ . • 




. 10 Traoe . oo;, 





.04 


.5 .:: 1.1 




8.8 








Limewater, cold at start 

Do 




o> .003 




.01 


.2 


1 


. 1 
.1 


LI 
















.04 


.002 .003 






.2 1 


. 1 


1.1 








A \ erageofO b - 














.4 6 


1.0 




3.4 























13 

Loss of matter in cooking potatoes — Continued. 





is 

s 

"o . 

&*£ 
"3 


Loss of matter in fresh 
potatoes. 


Percentage loss of each con- 
stituent. 


Method of preparation and 
cooking. 


© 

Is 
S 
>> 
u 

n 


IS? 


© 

"3 d 
_ ® 


c3 


.0* 


© 

Is 

g 

>> 


"8 a 

.9 § 

a o 


6 
"2 q 

o 
H 


© 

02 


«l 


C. Skins not removed — Cont'd. 

Distilled water, hot at start. . 
Do 


Grams. 
1,047 
1,075 


P.ct. 
0.15 
.16 


P.ct. 
0.001 
.001 


P.ct. 
0.005 
.008 


P.C«. 


P.ct. 
0.05 

.04 


Pc*. 
0.7 
.7 


P.c?. 
0.5 
.5 


Pert. 

1.3 
2.0 


P.c«. 


Pert. 
5.4 
4.4 












.16 .001 


.006 




.05 


.7 


.5 


1.6 




4.9 








Alkaline water, hot at start.. 
Do 


1,229 
1,034 


. 10 jtrace. 


.003 
.003 




.03 

.02 


.4 
.4 


.2 
.2 


.8 
.8 




3.2 

2.2 














.10 


t,race. 


.003 


.03 


.4 


.2 


.8 ; 


2.7 








Limewater, hot at start 

Do 


1,075 
848 


.04 
.06 


.001 
.001 


.002 
.003 


0.01 
.01 


.02 

.02 


.2 
.3 


.4 
.5 


.5 

.8 


0.1 
.1 


2.2 
2.2 










.05 


.001 


.002 


.01 


.02 


2 


.5 


.7 


•1 


2.2 








Average of 6 tests start- 














.4 


.4 


1.0 


.1 


3.3 

















The weight of each ingredient removed divided by the total weight 
of the same ingredient in the fresh potatoes before cooking gives the 
percentage of loss of that substance. These figures are shown in the 
last five columns of the table. The same composition was assumed for 
the peeled potatoes used in Experiment B as for the whole potatoes 
used in Experiment O. This may not be strictly accurate, since it pre- 
supposes the uniform composition of all parts of the potato. As shown 
on page 27, there is a slight variation between the composition of the 
interior and the part peeled off, but this probably is not great enough 
to have a material effect upon the results obtained. 

DISCUSSION OF RESULTS. 

By reference to the table (p. 12) it will be seen that, as might be 
expected, the greatest loss occurs when the potatoes are peeled and 
soaked in cold water before boiling. In this case the loss of nitroge- 
nous matter was from 46 to 58 per cent, depending upon the length of 
time they were soaked. Of the albuminoids 25 per cent and of the 
mineral matters 38 per cent were extracted by the water in which the 
potatoes were cooked. The water would ordinarily be thrown away 
and this material lost. 

When the potatoes are peeled and put into cold water, and heated 
to boiling as soon as possible, the loss is much smaller, being about 16 
per cent of the total nitrogenous matter (of which albuminoids form a 
trifle less than half) and about 19 per cent of the total mineral matter. 
When the potatoes are peeled and put directly into boiling water the 
loss of albuminoid and other nitrogenous matter is only about half 
that of the last case, but the amount of mineral matter is practically 



14 

the same. The boiling: water soon coagulates the albuminoids on the 
surface of the potato, rendering them insoluble. They fill the outer 

pores of the potato, rendering the inner juices less liable to loss, although 
not before a considerable amount of the salts or mineral matter has 
escaped. The relative amount of nonalbuminoid nitrogen lost is greater 

than when the potatoes are put into cold water at the start. There 
seemed to be but little difference as regards total nitrogenous matter, 
starch, and ash, whether distilled, alkaline, or lime water was used. 
The limewater, however, seemed to have a greater solvent action upon 

the albuminoids than did the distilled or alkaline waters. The solvent 
action of cold alkaline water was somewhat greater than that of dis- 
tilled water. Inasmuch as the albuminoid material of the potato is a 
globulin, 1 and globulins are insoluble in pure watei but soluble in saline 
water, this also is what would be expected. The salts in solution in the 
juice of the potato doubtless carry the globulin in solution to some 
extent, thus rendering a loss possible even in pure distilled water. 
The loss in boiling peeled potatoes is shown in graphic form in figure L, 




Fig. 4.— The composition of the potato and the lose of nutrients when boiled with the *kin 
removed: a, fiber, pectose, fat, etc. ; b, nonalbuminoid nitrogenous matter; <•. albuminoid nitn 

matter: </. mineral matter. The hatched portion represents tin- loss. 

It will be seen from the table that when the potatoes are unpeeled 
the loss of matter is very inconsiderable, less than 1 per cent of the 
albuminoid matter, only 1 per cent of the total nitrogenous matter, 
hardly a trace of starch, and but a little over 3 percent of the mineral 
matter being extracted. The different kinds of w atei- had no effect 

except on mineral matter. This was removed to a greater extent by 
the distilled water than by the alkaline or limewater. 



CONCLUSIONS. 

The conclusions drawn from these experiments may be briefly sum 
marized as follows: 

(1) In older to obtain the highest food value, potatoes should not be 
peeled before cooking. 

(2) When the potatoes are peeled before cooking, the least loss is 

sustained by putting them directly into hot water and boiling as rap 
idly as possible. Even then the loss is very considerable 



1 Osborne aud Campbell, Connecticut state st.i. Rpt. L895,p.255 E. S. K.,8,p.371), 



15 

(3) If potatoes are peeled and soaked in cold water before boiling 
the loss of nutrients is very great, being one fourth of all the albuminoid 
matter. In a bushel of potatoes the loss would be equivalent to a 
pound of sirloin steak. 

EXPERIMENTS WITH CARROTS. 

A series of experiments similar to those just described was under- 
taken with carrots. They were selected as fairly representative of the 
roots used for food. While in uncooked potatoes there is but a trace 
of sugar, such roots as beets, carrots, parsnips, etc., contain a con- 
siderable amount. This renders it probable at the outset that the 
loss in the cooking of carrots would be greater than in the cooking of 
potatoes. 

COMPOSITION OF CARROTS. 

Samples of the carrots used in the experiments were analyzed. The 
results of these analyses, as well as the average composition of carrots, 
including both American and European analyses, are shown in the 
following table: 

Composition of carrots. 







6 

'3 


a 






Carbohydrates. 












£> 


.• 








"2 A 


bD 






• 


u 






*« 








.9 bo 

a 


| 


d 




2 


M 




.O cc 








-2 




a 


£ 




<B 


."£ 


s 


%£ 


rpU 






























t 
























< 


H 


Ph 


Ph 


O 


P=H 


£ 


o 


H 


< 




P.ct. 


P.ct. 


P.ct. 


P.ct. 


P.ct. 


P.ct. 


P.ct. 


P.ct. 


P.ct. 


P.ct. 


P.ct. 


Carrots used in experiments ... 


87.5 


0.08 


0.18 


1.1 


(b) 


3.6 


3.0, (&) 


4.0 jclO.6 


0.8 


Average 17 American analyses di 88. 2 






1.1 


0.4 






9 2 


1.1 






1.2 


.3 


2.1 


4. 1 1.5 


3.0 10.7 


1.0 





















a 100 less the sum of the percentages of water, protein, fat, and ash. 

b Not determined. 

c Includes fat. 

d\J. S. Dept. Agr., Office of Experiment Stations Bui. 28. 

eKonig, Chemie der menschlichen Nahrungs- und Genussmittel, 3d ed., II, p. 649. 

Although carrots contain less nitrogen than potatoes, they seem to 
contain relatively more albuminoid nitrogen and therefore to furnish 
more matter available for building muscular tissue. In the carrots used 
in the following experiments, 44.4 per cent of the total nitrogen was in 
the albuminoid form. 

COOKING TESTS. 

In preparing carrots (sliced or whole) for the table they are put into 
either hot or cold water and boiled until they are soft enough to be 
easily pierced with a fork. The water in which the carrots have been 
boiled is usually drained off and thrown away. This water is colored 
yellow and has a very sweet taste, plainly indicating that some of the 
sugar has been extracted and lost. 

In order to determine how much food value was lost in boiling car- 



16 

rots under various conditions, twelve trials were made in which lime- 
water (bard Mater), alkaline water, and distilled water (soft water) 
were used. The carrots were prepared for cooking in the usual way by 
washing with a brash, scraping, drying quickly with a towel, and cat- 
ting into pieces. These pieces were wedge-shaped, usually about l 
inches long, and with three sides and a triangular base measuring 
about 1J inches on a side. In some of the trials tin- pieces were cat 
smaller and in some larger in order to determine the effect of si/e <>n 
the loss of material. As in the experiments with potatoes, the water 
in which the carrots were cooked was hot at the beginning of the cook- 
ing period in some of the tests and cold in others. The carrots were 
boiled in a metal kettle over a gas flame under as nearly the usual 
conditions as possible The loss of matter in cooking loo parts of 
fresh carrots and the percentages of each constituent lost in cooking 
under the various conditions are shown in the following table: 



Loss of matter in cooking oarroU. 





Weight <>r <:n-i'«.ts 

HSol. 


Loss of matter 
rarrots 


in fresh 


Percent 

-titnent. 


■ Oil- 


Method of preparation and 
coos 


Drj matter. 

nitrogen. 
Total aitro 


■7. 




= 


- 
\ - 

= - 
■- -.i 

- : 


= a 
- B 


7. 


.1 . Small J 

Alkaline water, hot at start.. 

Limewater, hoi at Btart 

Distilled water, cold at start.. 
Limewater, cold at Btart 


Grams. P.cL 
47*i 3. 93 


P.cL P.cL 
0.008 0.O8B 

.009 .064 

. 010 . 101 


P.cL 

1. 14 


: 
.::l 
.43 


I'.ct. 

3(1.5 
28. 4 


m. ii 

11.3 
1-.5 




P.cL P.cL 

53.0 J! . 

41.3 

27. 6 57. 3 


Average 


3.74 .008 


.(177 1.71 


. 36 -_"J. It 


Ki.:: 42.5 


2»>. (» 


47.3 


11. Mediumsia <l . 
Distilled w ater, hoi at Btart . . 

DO 


4'.'4 •_'. it.: .006 


.(•48 

(1.17 










Limewater, lint ;it start 

Alkaline water, hot at start.. 
Distilled water, <<>1<1 at Btart . . 
Alkaline water, cold at -tart .. 

On 


444 J 72 .006 .".v. 

; '. 1 . 58 

005 .050 

503 'J. 47 .1 

403 :;. 61 .003 .055 L82 


.::i 21.7 
US 21.4 6.2 -7 i 

• 


- 1 




2.95 .(Miy .050 1.75 


. 28 23. 5 <;. 4 27 


0. La 
Limewater, cold at start 




















L.02 











As will be Been, the character of the water makes little apparent 

difference in t he amount of nutrients lost when carrots are boiled. The 

Loss depends almost wholly upon the size of the pieces. The loss of 
mineral matter is large, being nearly one half of the total amount 
in the case of the small pieces, and nearly one-third of the total when 
the pieces were large. The loss of nitrogenous mutter and sugar is 

also very large. With small pieces about 10 per cent of the total 
nitrogen and 26 percent of the total sugar is lost, or about 1 pound 

of sugar in a bushel of carrot-. With medium size,! pieces the lo 



17 



nitrogen is 27 per cent and of sugar 26 per cent. With large pieces 
the loss of nitrogen is 20 per cent and of sugar 15 per cent. This latter 
loss is equivalent to over half a pound of sugar in a bushel of carrots. 
Of the total nutrients 30 per cent is lost from the 
small pieces, 24 per cent from the medium, and 20 
per cent from the large pieces. In other words, as 
ordinarily cooked carrots lose one- quarter of their 
nutritive value. Figure 5 shows these losses graph- 
ically. 

CONCLUSIONS. 

These trials suggest that in order to retain the 
greatest amount of nutrients in the cooking of 
carrots (1) the pieces should be large rather than 
small; (2) the boiling should be rapid in order to 
give less time for the solvent action of the water 
to act upon the food ingredients; (3) as little water 
as possible should be used; and (4) if the matter 
extracted be used as food along with the carrots, 
instead of being thrown away, the loss of 20 to 30 
per cent, or even more, of the total food value may 
be prevented. 

EXPERIMENTS WITH CABBAGE. 



Experiments analogous to those with potatoes 
and carrots were made with cabbage to determine 
the loss of food material during the process of 
preparation for the table. 

Cabbage may be taken as representing the class 
of pot herbs in which the leaves are the edible por- 
tion. It exposes more surface to the action of the 
water than do tubers or roots. 

COMPOSITION OF CABBAGE. 

The composition of the cabbage analyzed in 
connection with these experiments, as well as the 
average of American analyses of cabbage, is as 
follows : 

Composition of cabbage. 




Fig. 5. — The composition of 
the carrot and the loss of 
nutrients when boiled : a, 
fiber, starch, fat, etc.; b, 
sugar; c, nonalbuminoid 
nitrogenous matter; d, 
albuminoid nitrogenous 
matter; e, mineral mat- 
ter. The hatched portion 
represents the loss when 
medium-sized pieces were 
boiled, 



Albu- 
minoid 
nitro- 
gen. 



Total 
nitro- 
gen. 



Pro- 
tein. 



Carbohj'' 
drates. 



Cabbage used in these experiments . 
Average of 7 American analyses a... 



Per ct. 
92.5 
90.3 



Per ct. 
0.11 



Per ct. 
0.18 



Per ct. 
1.1 
2.1 



Per ct. 
0.7 
5..S 



Per ct. 
0.7 
1.4 



«U. S. Oept. Agr., Office of Experiment Stations Bui. 28. 

2103— No. 43 2 



18 



It will be noticed especially tbat in cabbage there is, relatively. 
much more albuminoid material than in either potatoes or carrots, the 
albuminoid nitrogen amounting to <">1 per cent of the total nitrogen. 

cooking n 

The plan of the experiments was the same as thai followed in the 
experiments with potatoes and carrots. In each trial half of a solid 
fair-sized cabbage was used. The cabbage was boiled in a metal kettle 
over a gas flame at about the same rate as on an ordinary cook stove. 
The following table shows the results obtained by the different methods 
of cooking: 

Loss of matter in cooking r«i>b<i<i< . 





- 


Loss of matter in I'i < -li 
oabo 


.-tit llellt. 


ooa 


Method <>f cooking. 


■ 

fat 

'Z 


1 

£ §§ 
1 || 

C = = 

- < 


1 

o 


: 

- - 

- 


r. 

r.ct. 

o. :;:; 
.34 


1M\ malt- i . 

Alliiimiiioi-I 
nil i 

Total d 


- s 

- - 
3*9 

- 
,..„. 

311 


i 

4 


Distilled water, cold at start. 
Do 


Gram*. 

471.7 
300. 1 


P.et. I'.rt. 
2.69 .009 


P.et. 

0.062 


P.et. 
1.76 

2.01 


P.et. 


- 


47.1 


Average 

Alkaline water, cold at start. 
Do 


2.58 .006 .<»5.> 

J 
317.5 3.08 .013 .065 


j 39 

•j. :;7 


.34 
.30 


34. 6 

41.2 


5. 5 82. 

1 IS 


47.8 










3.12 .(ill .073 2.38 
3.17 .005 .087 2.23 


. 20 
.40 

.38 


41. B 

42.4 

40.8 

41.6 


e 42. i 

- 1 

4.C 45 


40.7 


Limewater, cold at atari 

1),, 


331.1 
240. 4 


57.1 












3. 11 


.no.-, .1 - 










Average of 6 teal - in 




47 6 










.23 






Distilled water, hot at Btarl . 
Do 


2. 17 
•_'. 22 


.005 ."• 

M 1 . 65 




' 








2.20 .007 .057 1.60 

2.70 .on., .or,: •_•.]:; 
013 076 2.oi 


. 23 

.21 
.27 


20. 4 


f. (• :;i 


32. 9 




317.5 
263. 1 








Alkaline water, hot at start 
Do 




11 - 










2.75 .(HI .(>07 2.(Ht 


.24 
















Limewater, hot at -tart 

Do 


330/7 :: 05 ^006 ."71 2.21 






57. 1 






2. 04 . 006 


.(•70 






39. 2 












A\<ra_ 












7.0 























Even nnder the most favorable conditions the loss during the cook- 
ing of cabbage is very .meat, being 30 per cent of the total dry matter 
when distilled water is u>a] and as high as W) per cent when lime 

water is u^'d. In the latter case over one half of the mineral matter 

and over one third each of the carbohydrates and nitrogenous matter are 
dissolved out during- the process of cooking. The albuminoid matter 



19 




seems to be less soluble than any other of the substances present, there 
being but from 5 to 10 per cent of loss. Since albuminoids make up 
61 per cent of the total nitrogenous substances, it follows that with a 
loss of from 35 to 40 per cent of the total nitrogenous matter nearly all 
of the nonalbuminoid nitrogenous compounds must be dissolved out in 
the water in which the cabbage is cooked. It will be noticed that the 
loss of albuminoid nitrogen was much greater where alkaline water 
was used than with either 
distilled or limewater. The 
average loss in the cooking 
of cabbage is shown graph- 
ically in fig. 6. 

CONCLUSIONS. 



The kind of water used has 
more effect on the loss of 
nutrients in cooking cab- 
bage than the temperature 
of the water at which the 
cooking is started. In any 
case the loss is large. In 100 
pounds of uncooked cabbage 
there are but 7 J pounds of 
dry matter, and of this dry 
matter from 2J to 3 pounds 
are lost in the process of 
cooking. This loss seems to 

be unavoidable unless the cabbage is cooked in such a manner that 
the water in which it is boiled is also used. This is frequently the 
case when cabbage is cooked with corned beef. 

GENERAL SUMMARY. 

The losses which occur in cooking potatoes, carrots, and cabbage 
vary with the different methods of boiling followed, being quite con- 
siderable in some cases. These losses must be taken into account in 
computing dietaries and made good by adding other materials to sup- 
ply the nutrients lost. While the loss is not so great as to render 
it imperative that people in comfortable circumstances should aban- 
don methods of preparing these foods which they consider make them 
most palatable, there are very large numbers who can not afford to 
permit even the comparatively small waste of food observed in these 
experiments. 

The purpose of experiments, such as those here reported, is to learn 
what actually takes place in the process of preparing food by the com- 
mon methods. Those having charge of the preparation of food must 
determine how far it is desirable under individual circumstances to 
apply the information obtained. 



ElG. 6.— The composition of the cabhage and the loss of 
nutrients when boiled : a, starch, sugar, fiber, fat, etc. ; 
b, nonalbuminoid nitrogenous matter; c, albuminoid 
nitrogenous matter; d, mineral matter. The hatched 
portion represents the loss. 



THE DIGESTIBILITY OF POTATOES AND EGGS. 

By H. snvi.kk. B. 8., 

Che mis t, Minnesota Agricultural Experiment 8tation, and Profeesorof Agricultural 
Ghcmistru, College of Agriculture, University of Minm 

INTRODUCTION. 

There seems to be a very wide difference of opinion regarding the 
digestibility of the potato, some considering it a very easily dig* 
food and others a food digested with some difficulty. The information 
on which such opinions are based is comparatively limited. Our knowl- 
edge concerning the digestibility of food is quite largely based on artifi- 
cial digestion experiments. The number of experiments made with man 
is comparatively small. An experiment with man on the digestibility 
of potatoes was made by Kubner and reported some years ago. 1 

More work of this nature seemed desirable, therefore an experiment 
was undertaken with a healthy man in which potatoes formed the 
principal article of diet. Potatoes being almost entirely a farinaceous 
food, it was necessary to have some easily digested albuminoids in the 
dietary and also some fat, since previous digestion experiments in this 
laboratory have indicated that in order to obtain normal digestion it is 
necessary to use a well-balanced ration supplying a sufficient amount 
of nitrogenous material for replenishing the waste tissues of the body. 
To furnish this nitrogenous matter and fat hard boiled eggs were 
added. Upon trial the diet of potatoes and e^^s proved an unnatural 
and distasteful one to the subject and it was found necessary to add 
some milk and a little cream to the dietary in order to make it well 
balanced and palatable. 

The digestibility of the eggs was first determined by the Stutter 
method of artificial digestion, to learn something of the effect of boil- 
ing for various periods. Such knowledge was considered essential in 
the interpretation of the results of the experiments with man. The 
digestibility of the milk ami cream were assumed as described beyond. 

DIGESTIBILITY ()F BOILED BOGS IN PEPSIN SOLI TI«>.\. 

Five experiments were made to determine the digestibility oi 

cooked under ditfe rent conditions. A pepsin solution was prepared 
consisting of 1.1 parts of pepsin and 7.6 parts of hydrochloric acid in 



'Ztschr. Biol.. 187U, p. 147. U. S. Dept. Agr., I tfflec of Experiment Stations Bol 

21, p. tio. 
20 



21 

500 parts of water. This solution dissolved 50 parts of hard-boiled 
egg albumen in six and one-half hours at a temperature of from 38° 
to 40° C. 

Eggs were cooked for 3 minutes at 100° 0., giving a " soft-boiled " egg, 
and for 5 minutes and 20 minutes at the same temperature. One egg 
boiled 3 minutes and digested for 5 hours in about 200 cc. of pepsin 
solution as prepared above, compared with one boiled 20 minutes and 
treated in the same way, showed 8.3 per cent undigested nitrogen in 
the former, against 4.1 per cent undigested nitrogen in the latter. 
Under similar treatment the egg boiled 5 minutes gave 3.9 per cent 
undigested nitrogen. 

Another trial was then made, in which the eggs were cooked for 
periods of 5 and 10 minutes in water at 82.2° O. (180° F.) In both of 
these cases the nitrogen was entirely digested in 5 hours. The results 
are given in the following table : 



Eesult of digesting boiled eggs 5 hours 


in pepsin solution. 


No. of 
experi- 
ment. 


Length 
of time 
cooked. 


Tempera- 
ture at 
which 
cooked. 


Weight 
egg used 
(without 

shell) . 


Total 
nitrogen 
in fresh 

eggs. 


Total 
undi- 
gested 
nitrogen. 


Total 
nitrogen 
digested. 


Pepsin 

solution 

used. 


1 
2 
3 
4 
5 


Minutes. 
5 

10 
3 
5 

20 


Beg. F. 
180 

180 
212 
212 
212 


Grams. 
39.34 
47.02 
38.67 
43.80 
40.64 


Grams. 

.944 
1.128 

.929 
1.050 

.960 


Grams. 


Per cent. 
100.0 
100.0 
91.7 
96.1 
95.8 


Cc. 
197 
235 
193 
219 
203 




6. 0768 
.0408 
.0408 



From the above it seems probable that while the method of cooking 
has some effect upon the rate of digestibility it does not materially 
affect the total digestibility. These results agree quite closely with 
those obtained by Eubner. 1 In an experiment with man he found that 
97.1 per cent of the nitrogen of hard-boiled eggs was digested. 

DIGESTION EXPERIMENT ON MAN WITH A DIET OF POTATOES, EGGS, 
MILK, AND CREAM. 

The subject of the digestion experiment was a healthy man, 22 years 
old. He was a laboratory assistant, and his work did not demand a 
great amount of muscular exercise. The experiment began with dinner 
May 14, 1896, and ended after dinner May 18, covering 13 meals, or 4^ 
days. The weight of the subject (without clothing) at the beginning 
of the experiment was 62.5 kilograms (137 J pounds) and at the end 
62.6 kilograms (137f pounds). 

The daily dietary as finally adopted consisted of 1587.6 grams (3J 
pounds) of potatoes, 8 eggs, 710 cubic centimeters (1J pints) of milk, 
and 237 cubic centimeters (J pint) of cream. The latter was necessary 
in order to supply fat to raise the fuel value of the food to the desired 

^tschr. Biol., 1879, p. 128. U. S. Dept. Agr., Office of Experiment Stations Bui. 
21, p. 61. 



22 



point. The approximate amounts and the composition of each food 
consumed per day are shown in the following table: 

Amount anil composition of preliminary daily dirt. 



Solid 
matter. 




Protein. 


,.-.,, Carbo- 
la ' hydrates. 


Ufa F "*' 1 

\al.U-. 


drums. 

Potatoes fl,587 ^rnms) 

Eggs (8 hard boiled) 118.40 


<i mms. 

8.18 

4.08 
.91 


Oram* 

50.80 
25.40 


0.45 


14..M 1 M 


Milk (710 cubic centimeters) . 

Cream (287 cabiccentimeters) . 40.82 




27. 22 30. 39 

• 




Total 807.82 10.5H 


121. 56 110.68 



This diet was given for three days before the experiment began in 
order that the body might get into equilibrium with it. 

After breakfast on the day the experiment commenced and after din- 
ner on the day it closed some charcoal in gelatin capsules was taken, 

in order to identify the frees belonging to the food of the experiment 
proper. The fresh feces weighed on an average 204 grams per i\ay and 
the urine 1,108 grams. The food, urine, and U'ccs were analyzed. The 
composition of the total fond eaten and of the total feces, together with 
the nutrients contained in the food eaten and lost in the feces and the 
percentage of each nutrient digested, are shown in the following tables: 
Weight and composition of food eaten and of feces for four and one-third days. 



Potatoes . 

Milk 

Cream — 



Weight. 



Total 
organic 
matter. 



6.380 

23. 86 
2,722 12.27 

17.41 
a 206 82. ■■•■■'> 



, Protein. 


Fat. 


/'• r cent. 


/'. /■ -•• nt. 


9.50 


- 


12.63 


11.23 


:;. 25 


4.ol 


1.69 


1. 




14.80 



Carbohy- 



5.01 

1.72 

b41. 17 



Fn. I 
\ aloe 

Ash. 

gran, 

rali II 
lit.-.l 

I 

i HI 

L6 27 ; 



ft Water-free substance. 

bOne and four-tenths per cent is allowed for biliary products. < arbol 
Fat Ash + 1.40). 

Weights and fuel values of nutrients in food eaten and In fec< and one third 

days; and weights, fuel value, and percentage* of nutrients du 





Total 

matter. 


Pro* in 




Carbohj 




Fuel 






159.5 




. 




' 






.-. z a 


227.4 


127. 1 










Milk 














Total eggs, milk, and cream 


931.5 


3:a.2 


4.18.3 


152.0 


42. 3 


r> 580 


Total, from whole food 

Fuel value < f an : 


2, 315. 5 


490.7 
























160.9 
2 145. 6 

92. 7 


111.7 

88.8 

71. :i 




93.0 


■ 




Amount digested in whole food 
Amount eggs, milk, ami cream • 
▲mount potatoes digested 

Pex tint digested of whole food 




1 













rrAn unknown amount of salt was eaten, which renders the amount ..t mineral mattei 
Bomewhat doubtful. 



23 

In calculating the amount of nutrients furnished by the eggs, milk, 
and cream that were digested, it is assumed that 07 per cent of the 
protein and all of the carbohydrates (chiefly milk sugar) in these foods 
were digested. Inasmuch as the amount of fat in the potato is so 
extremely small, no attempt was made to calculate its digestibility. 
The figures for the digestibility of the whole food (93 per cent) practi- 
cally represent the digestibility of the fat in the eggs, milk, and cream. 
The amount of nutrients digested in the eggs, milk, and cream 
deducted from the total digested nutrients gives the nutrients digested 
from the potato. The percentages digested were calculated from these 
amounts. In calculating the fuel value 1 gram of protein is assumed 
to yield 5.5 calories, 1 gram of fat 9.3 calories, and 1 gram of carbohy- 
drates 4.1 calories. Nitrogenous matter is not as completely oxidized 
in the body as when burned in the air, 1 since it is largely excreted in the 
form of urea. Urea contains some energy, which is, however, unavail- 
able to the body. Briefly, the fuel value of urea is calculated as 
follows: 2 

M protein 



6.25 



X 2.143 x 2.53=fuel value of urea. 



This may be reduced to the simpler form, M protein x 0.87=fuel 
value of urea. 

More or less salt was eaten of which no account was made, therefore 
the digestibility of the ash is not calculated. It is of comparatively 
little importance, since to some extent at least the soluble mineral 
matters, e. g., salt, pass directly to the kidneys, from which they may 
be secreted within a few hours after being taken into the stomach. 

DISCUSSION OF RESULTS. 

From the results of this experiment it would seem that while the 
nitrogenous matter is not very completely digested, the digestibility of 
the carbohydrates is quite high. Since the potato consists very largely 
of carbohydrates, it may be regarded, at least in the case of the per- 
son here experimented with, as a food which is well digested. The 
results obtained in this experiment agree very closely with those 
obtained by Eubner (see p. 21), as will be seen by the following com- 
parison : 

The digestibility of potatoes as determined by American and European investigators. 



I Protein 
j digested. 



Carbohy- 
drates 
digested. 



The author's experiment . 
Rubner's experiment 



Per cent. Per cent. 



71.9 
67. 



93.0 
92.4 



l \J. S. Dept. Agr., Office of Experiment Stations Bnl. 21, p. 103. 
Connecticut Storrs Sta. Ept. 1891, p. 125. 



24 



The nitrogen balance, — The urine was collected daring the period cov- 
ered by the digestion experiment, and the total of solids, nitrogen, and 

ash in it determined. In this way a balance of income and outgo <>t 
nitrogen could be obtained and t lie resultant gain <>r loss of protein 
calculated. The amount of urine excreted during the period covered 
by the experiment was 4,800 grams. It contained 6.18 per cent of 
water-free Bubstance, L42 percent of nitrogen, and 1.63 per cent of ash. 
The gain or loss of nitrogen and the calculated gain or loss of protein 
per day are shown in the following table: 

Balance oj inconu and outgo of nitrogen and gain of protein. 



Quantities for \\ hole period (4^ days)... 
Quantities per day ' 



Nitrogen Nitrogen 
in food, in feces. 



78.51 
18.14 



Grams. 
B.77 



Nitrogen Nitrogen 

d. in urine, gained. 



Grams. 
89.74 

16.11 



1.-..74 






Protein 
gained. 



During the experiment the subject gained 9.88 grams one third of 
an ounce) of protein. Assuming that muscle contained L'3 per cent of 
protein, the subject gained 43 grams of muscle, or about lj ounces. 



THE COMPOSITION OF DIFFERENT PARTS OF THE POTATO AND 

THE LOSS OF NUTRIENTS DURING THE PROCESS OF BOILING. 

By Almah J. Fkisby, M. D. ; and A. P. Bryant, M. S. 

INTRODUCTION. 

The potato is composed of three parts, which may for convenience be 
termed outer skin, inner skin, and flesh. The outer or true skin is dry 
in appearance, usually grayish brown in color and corresponds to the 
bark of the rest of the plant. The portion lying immediately beneath 
the skin is slightly colored, containing whatever coloring matter may 
be present in the potato, and is the part which turns green on continued 



b cL 



c W*Mt 



V 



v 



Pig. 7. — Transverse and longitudinal sections of the potato (after Condon and Bussard) : a. skin; 
b, cortical layer ; c, outer medullary layer ; d, inner medullary layer. 

exposure to the sunlight, giving a strong unpleasant taste to the potato. 
This portion has some resemblance to the skin in general appearance, 
and is usually removed with the skin in preparing potatoes for the 
table. Its true name is the rlbro-yascular layer, but it is also some- 
times designated as the herbaceous or cortical layer, subcutaneous por- 
tion, and inner skin (see fig. 7). The main bulk of the potato is composed 



20 

filled with starch grains and a little nitrogenous matter, and may Km 
designated as the flesh of the potato. 

[Shortly alter the completion of the present bulletin an extended 
study of potatoes was reported by fl. Condon and L. Bussard. 1 The 

authors investigated the botanical structure of a large number of vari- 
eties of potatoes and determined the relative compositi f large, 

medium, and small potatoes and of the different parts of the tubers. 
The taste and culinary properties of a number of standard varieties 
were also investigated. The potatoes were cooked in several ways. 
Among the conclusions reached by the authors were the follow ing: In 
judging the value of a variety of potatoes analyses should be made ofi 
number of entire tubers. The culinary value of the potato is directly 
proportional to its nitrogen content and inversely proportional to its 
starch content. The different varieties of potatoes were found to vai y 
greatly in their resistance to boiling, some retaining their form com- 
pletely, while others were almost entirely disintegrated. In the 
authors opinion the resistance to boiling did not depend upon the eon- 
tent of pectin or starch, but seemed to depend principally upon the 
relative proportion of albuminoids present. No definite relation was 
observed between chemical composition and early maturity. < Generally 
speaking, the early varieties contained more water and nitrogenous 
material and less starch than the late varieties. The number of excep- 
tions was, however, large.] 

In order to ascertain to some extent the variation in composition of 
the different parts of the tuber a quantity of smooth potatoes of aver 
age size was obtained and analyses of the different parts made. The 
variety selected was that known as the "White Star." 

COMPOSITION OF DIFFERENT PARTS OF JIN. POTATO. 



Twelve medium-sized potatoes of known weight were taken. The 
skin was carefully removed by scraping with a knife and the skin and 
potatoes weighed. The sum of the weights of the scraped potatoes 
and of the skins did not equal the weight of the potatoes ;it tin' start. 
More or Less water had evaporated from the moist surfaces. It was 
assumed that hair of the Loss came from the skins and half from the 
smooth surface of the scraped potatoes, inasmuch as the amount of 
surface freshly exposed to the air was the same in the two portions. 
The inner skin of the potatoes, or Qbro-vascular layer, was next 
removed by scraping, care being taken to include as little flesh of the 
potato as possible. The amount removed l>\ this operation was w e 
as before and the Loss of water during the process divided equally 
between the part removed and the part remaining, i. e., the flesh. The 
three portions were dried at LOO ('.and this partially dried material 



1 Ann. s, i. Agron., 1897, I. No. l'. p. l'"-". 




27 

of cells was analyzed. The weights of the different parts and their 
proportion of the whole potato were as follows : 

Proportions of different parts of the potato. 

Weight I Per cent 
in grams. j of -whole. 

Twelve unpeeled potatoes 

Outer, or true, skin 

Inner skin or fibro-vascular la vera 

Flesh 

a Including a small amount of flesh. 

THE ANALYSES. 

Water, nitrogen, fat, and ash were determined by the usual methods. 
Crude fiber was determined in the fibro-vascular layer and the flesh, 
but there was so little of the skin left after making the other deter- 
minations that the estimation of fiber could not be made. Ifc would, 
however, presumably be quite high. 

The nitrogen of the potato is not all in the form of true albuminoids 
or proteids, but nearly half is in the form of amido compounds, includ- 
ing, principally, asparagin. 1 Inasmuch as the amount of nitrogenous 
material in the potato is small, and the amido compounds can neither 
build tissue nor repair waste as do the albuminoids, the nutritive 
value of the nitrogenous substance (protein) of the potato is very small. 
In the experiments here reported the albuminoid nitrogen was deter- 
mined by Stutzer's method. 

The composition of different parts and the calculated composition of 
whole potatoes here analyzed as compared with results of other Ameri- 
can and European analyses are shown in the following table : 

Composition of the whole potato and its different parts. 



Nitrogen. 



Albu- 
minoid 



Pro- 
tein. 



Nitro- 
gen-free 
extract. 



Carbohydrates. 



Outer, or true, skin 

Inner skin or fibro-vascular layer. . 
Flesh 

Calculated composition of whole 
potato 

Average of 80 American analyses a 
Average of 178 European analyses b 



83.2 
81.1 



78.0 
75.0 



Per ct. 
0.25 
.24 

.18 

.19 



Per ct. 
0.43 
.36 
.32 

.32 
.35 



Per ct. 
2.7 
2.3 
2.0 

2.0 
2.2 
2.1 



Per ct. 
0.8 



Per ct. Per ct. ' Per ct. 

14. 6 1. 8 

12. 6 1 0. 7 1.1 



15.7 
18.8 
21.0 I 



.9 
1.1 



a From an unpublished compilation of analyses of American food products. 
frKonig, Chemie der Nahrungs- und Genussmittel, 3d ed., II, p. 626. 

Although of fine appearance, the potatoes used in the present experi- 
ment contained an unusually small amount of dry matter and a large 
proportion of water, as will be seen by comparing their chemical com- 

1 Schulze, Barbieri, and Eugster, Land. Vers. Stat., 21 (1878), p. 63; 27 (1882), p. 357. 
See also Konig, Chemie der inenschlichen Nahrungs- und Genussmittel, 3d ed., II, 
p. 631. 



2R 

position with that of average potatoes. Whether this was due to the 
variety or to the year is a matter of doubt. The skin, although appar- 
ently very dry, contained nearly as large a percentage of water as the 
rest of the potato. The portion immediately under the true Bkin, i. <-.. 
the libro-vascular layer, contained the greatest amonnt of water. 
Payen 1 states that the epidermis and the herbaceous portion imme 
diately below it contain little or no starch deposit. The above results 
sccin to be in accord with this, though no estimation of standi itself 
was made. It will be noticed that the skin contains about 10 per emit 
more albuminoid nitrogen than the flesh, and more than twice the 
amount of mineral matter (ash). One of the most noticeable differ- 
ences is the relatively large amount of ether extract in the skin — nearly 
1 per cent. This had much the appearance of wax. and had an odor 
slightly resembling that of beeswax. 

THE PROTEIN l.\< rOR, 

The protein was determined as usual by multiplying the total nitro- 
gen by the factor G.2o. This factor is based on the assumption that 
there is on the average 1G per cent of nitrogen in protein. In tie case 
of potatoes the results thus obtained are considerably too large. In 
the first place, the nonalbnminoid compounds have a much larger 
proportion of nitrogen than do the albuminoids, and consequently 
should be obtained by the use of a much smaller factor than 6.25. 
Besides this, the albuminoids themselves contain slightly more than 
1<> percent of nitrogen. Osborne and Campbell 2 have investigated the 
proteid of the potato, which they propose to call " tuberin," and find 
that it contains 16.24 per cent of nitrogen. 

For the present purpose it will be convenient to assume that all the 
nonalbnminoid nitrogen of the potato occurs in forms more or less sim- 
ilar to asparagin. Asparagin contains 21.21 per cent of nitrogen. The 
average amount of albuminoid nitrogen in potatoes is oi; percent of 
the whole, which is the same proportion as was found in the flesh of 
the potatoes used in these experiments. Assuming ~>n' per cent of the 
nitrogen of the potato to belong to albuminoid nitrogenous matter 
(tuberin) and the remaining II per cent of the nitrogen to belong to 
nonalbuminoid nitrogenous matter (asparagin), there will be an aver* 
age of 18.42 per cent of nitrogen in the nitrogenous subst&nce of the 
potato. This corresponds to the facto]' 5.43. 

In round numbers, therefore, 5.5 may be taken as the factor by which 
the total nitrogen of the potato should be multiplied in order to obtain 
the total nitrogenous matter <>r protein. While the change made by 
using this instead of the ordinary factor 6.25 for calculating the protein 

is slight, it would amount to aboul a gram of protein per day in the 
case of a person eating old grams , { pound of potatoes daily. The 



Substances alimentaires, p. 305. 
• Connect Lout State Sta. Bpt. L895 3 p. 256 E. S. EL, B, p. Ml). 



29 

difference in composition as computed by using the factor 5.5 for calculat- 
ing protein instead of the factor 6.25 is shown in the following table : 

Comparison of the composition of the potato when the factor 5.5 is used instead of the 
factor 6.25 in calculating protein. 



Outer, or true, skin 

Inner skin or fibro-vascular layer.. 

Flesh 

Calculated composition of whole 

potato 

Average of 86 American analyses. 



Nitrogen 
X 5.5. 



Per ct. 
80.1 
83.2 

81.1 

81.3 



Per cent. 
2.4 
2.0 
1.8 

1.8 
1.9 



Nitrogen 
X G.25. 



Per cent, 
2.7 
2.3 
2.0 

2.0 
2.2 



When 
protein 

= NX 5.5, 



Carbohydrates by 
difference, a 



When 
protein 

= NX 6.25. 



Per cent. 
14.9 
13.6 
16.2 

15.9 



13.3 
16.0 



15.7 

18.8 



a 100 less the sum of the percentages of water, protein, fat, and ash. 
AMOUNT OF SOLID MATTER IN THE JUICE OF THE POTATO. 

When we consider the amount of water in the potato, it is to be 
expected that a considerable portion of the ingredients maybe in solu- 
tion. If a potato be grated and the juice pressed through a linen cloth 
a large amount of dark-colored liquid is obtained having an acid char- 
acter. This acidity is commonly said to be chiefly due to citric acid with 
more or less tartaric and succinic acids. The mineral water is very 
largely in the form of potash salts, soluble in water. The asparagin 
present is also soluble in water, and the tuberin more or less soluble in 
the acid. The following table shows the percentages of the different 
substances found in the juice of the potato and in the solid matter: 

Distribution of material in the solid matter and juice of the potato, a 





Dry 

matter. 


Nitrogen. 






Albumi- 
noid. 


Non albu- 
minoid. 


Albumi- 
noid -f 

nonalbu- 
minoid. 


Ash. 




Per cent. 
85 
15 


Per. cent. 
15 
49 


Per cent. 

36 


Per cent. 
15 
85 


Per cent. 
15 




85 






Total 


100 


64 


36 


100 


10G 







a Lawes and Gilbert, On the Growth of the Potato, p. 26, Eothamsted Memoirs, vol. ( 



LOSS OF NUTRIENTS IN BOILING. 

Since 85 per cent of the nitrogenous matter and 85 per cent of the 
mineral matter are in a state of solution in the potato, it would seem 
quite probable that there might be a considerable loss of these sub- 
stances during the process of preparing potatoes for the table. Experi- 
ments were therefore made to investigate this loss and determine its 



30 



amount. Four trials were made, (1) with the skins removed, the peeled 

potatoes being put in cold water, which was heated at once over ;i 
moderate name; (2) with the skins removed, the peeled potatoes placed 
directly in boiling water; (3) with the skins on, the potatoes being put 
in cold water, which was heated as in the first ease: and (4 with the 
skins on, the potatoes being placed directly in hoi water as iii the sec- 
ond case. Six medium sized potatoes wen- used for each trial. They 
were boiled in one liter of distilled water in an aluminum kettle until 
they were easily piereed with a fork. The kettle was then removed 
from the fire, the water poured off, and the potatoes rinsed with dis 
tilled water. It was found that the potatoes in every case except the 
second gained slightly in weight during tin- process of cooking. This 
gain was evidently due to water absorbed. 

The water in which the potatoes were boiled, united with that 
used in rinsing them after boiling, was made up to a definite volume 
by adding distilled water. Aliquot portions were taken for analysis. 
fhe cooked potatoes were also dried and analyzed. In most cases the 
amount of each substance found by analysis in the water used in cook- 
ing them, added to the amount of the same substance found in the 
cooked potatoes, gave, within the limits of analytical error, the total 
amount of that substance calculated as being present in the raw 
potatoes. The weight of any substance found in the water used in 
cooking the potatoes divided by the weight of that same substance 
calculated as being present in the uncooked potatoes gave the per- 
centage of loss during boiling. The loss of carbohydrates wae 
mated by subtracting the sum of the protein losl calculated by multi- 
plying the total nitrogen lost by 5.5) and the mineral matter Lost from 
the total loss of dry matter. 

The following table gives the loss of nutrients when the potatoes 
were cooked in different ways: 

The lost of mat> rial <hirin<j the pro- • 





Dry 

ni.itu-r. 






«lr..t. - 






Albumi- 
noid. 


Nonalbu- 

iniliniil. 






Skin* n : ■ii'liiti. 
Did ai beginning "i t . -r 


3.7 
LC 


3.3 


12 t 
IT B 


- 
10. fl 




i: <• 








3.9 




15. 4 












Water cold .it beginning <•( test 


.3 
.3 


4 


1 7 


.6 
1.0 


.1 












.3 


5 


.8 

















It will be seen that the Loss of matter during the process of cooking 
was confined quite largely to the nitrogenous Bubstances and the min- 
eral matter. The total loss of dry matter, however, was in some 



31 

considerable, indicating a loss of starch and other carbohydrates. The 
loss of nitrogen and mineral matter is easily explained by supposing 
that substances which were dissolved in the juices simply passed out 
into the water. The loss of the carbohydrates, on the other hand, is 
probably largely mechanical. 

It will be noticed that the calculated loss of carbohydrates was 
almost nothing when the potatoes were protected by their skins. 
When the skins were removed before cooking, more or less of the 
softened and broken cell walls and swollen starch grains were abraded 
during the process of boiling. Although this process is mechanical, 
the material removed is just as truly lost as if an equivalent amount 
of starch had been converted into dextrin during the boiling and then 
dissolved. Possibly there is a slight loss of starch which is chemical 
rather than mechanical. In roots, such as beets, turnips, and carrots, 
there is more or less sugar which might dissolve out, but the fresh 
potato contains practically no sugar. 

CONCLUSIONS. 

When potatoes are boiled with the skins removed, there is a very 
considerable loss not only of organic nutrients but also of mineral salts. 
These salts, while not nutrients in the sense in which this term is fre- 
quently used, are nevertheless important in nutrition. They are of 
especial value, because of the potassium compounds which they con- 
tain, and are apparently necessary for health. 

The greatest actual loss of nutrients seems to be due to the mechan- 
ical abrasion of the soft outer portions of the potato while cooking. 
In this case nearly 3 per cent of the carbohydrates and 4 per cent of 
the available flesh-forming nitrogenous matter are lost. When the 
potatoes are boiled with their skins on, the loss of nutrients is very 
slight, consisting chiefly of nonalbuminoid nitrogenous substances and 
mineral matter. It is self-evident that if it is desired to boil potatoes 
with as little loss as possible the skins should be left on. 



X>f 



